Method and System for Recovering Oil and Generating Steam from Produced Water

ABSTRACT

A method of recovering oil from an oil well and producing steam for injection into an injection well is provided. After recovering an oil-water mixture from the oil well, oil is separated from the mixture to produce an oil product and produced water. In one process, the produced water is directed to an indirect fired steam generator which is powered by an independent boiler or steam generator. As water moves through the indirect fired steam generator, the same is heated to produce a steam-water mixture. The steam-water mixture is directed to the steam separator which separates the steam-water mixture into steam and water. The separated water is directed from the steam separator back to and through the indirect fired steam generator. This separated water is continued to be recycled through the indirect fired steam generator. Steam separated by the steam separator is directed into the injection well.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(e) from thefollowing U.S. provisional application: application Ser. No. 61/150,598filed on Feb. 6, 2009. That application is incorporated in its entiretyby reference herein.

BACKGROUND OF THE INVENTION

Oil producers utilize different means to produce steam for injectioninto the oil bearing formation. The steam that is injected into thegeologic formation condenses by direct contact heat exchange, thusheating the oil and reducing its viscosity. The condensed steam and oilare collected in the producing well and pumped to the surface. Thisoil/water mixture, once the oil has been separated from it, is what isreferred to as ‘produced water’ in the oil industry.

Since water can comprise up to 90% of every barrel of oil/water mixtureremoved from the formation, the recovery and reuse of the water isnecessary to control the cost of the operation and to minimize theenvironmental impact of consuming raw fresh water and subsequentlygenerating wastewater for disposal. Once the decision to recover wateris made, then treatment of those produced waters is required to reducethe scaling and/or organic fouling tendency of the water. This treatmentgenerally requires the removal of the hardness and other ions present inthe stream, preferably to near zero. As is understood in the art, the‘hardness’ causing ions are the combined calcium and magnesium salts inthe water to be used in steam generation equipment and is typicallyexpressed as parts per million (ppm) although other terms can be used.While silica is not considered as adding to the hardness value, itspresence can also lead to scaling problems if present in other thanminimal amounts.

The traditional method for generation of steam in enhanced oil recoveryis to utilize a once-through steam generator (OTSG) in which steam isgenerated from a treated feedwater through tubes heated by gas or oilburners. The OTSG feedwater can have a total dissolved solidsconcentration as high as 8,000 ppm, but requires a hardness level thatis 0.5 ppm (as CaCO3) or less. This method produces a low quality or wetsteam, which is approximately 80% vapor and 20% liquid, at pressuresranging from 250 pounds per square inch gauge (psig) up to 2400 psig.This 80% quality steam either directly injected into the formation or insame cases the 80% vapor is separated from the 20% water and then thevapor is injected into the formation. Either a portion or all of the 20%blowdown is disposed as a wastewater.

Another method that has been used to obtain the high quality steamrequirement is using a water tube boiler instead of the OTSG to generatesteam. The water tube boiler, however, requires an even greater amountof feedwater pretreatment than the OTSG to ensure problem freeoperation. The lime soda softening, media filter, and polishing WAC arereplaced by a mechanical vapor compressor evaporator (MVC). A very largeelectrical infrastructure is required. to supply power to the MVCevaporator compressors and power consumption is high due to MVCevaporator compressor. The concentrate from the evaporator in the caseof high pH operation is difficult to process, requiring expensivecrystallizers and dryers or expensive offsite disposal.

SUMMARY OF THE INVENTION

The present invention provides a novel high pressure steam generationmethod and apparatus for produced water that eliminates the need foronce through steam generators and power consuming vapor compressors.

The present invention includes a system and process where produced waterfrom an oil recovery process is heated by various heat sources and thendirected into a steam separator that separates the water from the steam.The separated water from the steam separator is directed through one ormore coiled pipes that extend through one or more containment vessels orchambers that form a part of an indirect fired steam generator. Steamfor heating the water in the coiled pipes is generated in a firedboiler, such as a water tube boiler, and the generated steam is directedinto the containment vessel where the steam, which is held in thecontainment vessel, heats the water passing through the coiled pipes.This essentially heats at least some of the water passing through thecoiled pipes to produce a steam-water mixture that is directed back to asteam separator. This process is continuous and is effective to produceapproximately 98%-100% quality steam.

The apparatus is capable of operating at high pressures and can beeconomically fabricated and cleaned using conventional pipe “pigging”equipment.

In a process for producing high pressure steam vapor, de-oiled producedwater that has a quality similar to that of OTSG feedwater is used asfeedwater for an indirect fired steam generator (IFSG). The IFSG is anapparatus that provides an economic and robust method to produce highpressure steam. The IFSG consists of a number of vessels that typicallyhave one heat transfer pipe in a containment vessel. Each pipe follows aserpentine path, forming a coil, inside each containment, vessel so thatthe amount of heat transfer coil in each containment vessel is maximized(See FIGS. 2 and 3). Multiple vessels can be joined in parallel to forma bank. Multiple banks can be joined to form a grouping. The desiredsteam generation capacity is achieved by optimizing the number of banksand groups.

The preferred design used in the present invention provides a producedwater steam generation plant that overcomes a number of problems.

First, the problem prone low efficiency once through steam generatorsfor high pressure steam production using treated produced water is nolonger required.

Second, the pretreatment requirements of the produced water, prior tohigh pressure steam generation, are minimized. Sludge streams associatedwith warm lime softening are eliminated.

Third, the process as disclosed herein, is steam driven and there is norequirement for high energy consuming mechanical vapor compressors orelectrical infrastructure.

Fourth, controlled levels of multivalent cations, combined withcontrolled levels of silica, substantially eliminates the precipitationof scale forming compounds associated with sulfate, carbonate, orsilicate anions. Thus, cleaning requirements are minimized. This isimportant commercially because it enables a water treatment plant toavoid lost water production, which would otherwise undesirably requireincreased treatment plant size to accommodate for the lost productionduring cleaning cycles.

Fifth, the apparatus can be cleaned by “pigging”, which is commonly usedfor OTSGs.

Sixth, another benefit to the IFSG operation is the use of industryaccepted water tube boilers, the feed to which is not organic ladentreated produced water.

Seventh, if OTSGs are used to generate the steam required to drive theIFSG, the OTSGs are operated using feedwater that meets the guidelinesof the various national and international standards.

Finally, the IFSG steam generation process has the benefits of a veryhigh brine recirculation rate to evaporation rate ratio, which resultsin better heat transfer surface wetting, and a lower temperaturedifference combined with a lower unit heat transfer rate across the heattransfer surface than an OTSG operating on the same produced water. Theresult is a better design with less scaling potential and higherallowable concentration factors.

Other objects and advantages of the present invention will becomeapparent and obvious from a study of the following description and theaccompanying drawings which are merely illustrative of such invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram that shows the use of the IFSG process.

FIG. 1A is a schematic diagram showing an alternative process using theIFSG process.

FIG. 2 is a perspective view of an IFSG with portions broken away tobetter illustrate the heating tubes of the IFSG.

FIG. 3 is an illustration showing a bank of IFSGs interconnected.

DETAILED DESCRIPTION OF THE INVENTION

The invention disclosed herein provides an integrated process andapparatus for generating high pressure steam from produced water inheavy oil recovery operations. The energy that would normally only beused once to generate injection steam is used twice in this process. Thefirst use of the energy is the generation of steam from high puritywater in a direct fired water tube boiler. The second use is thegeneration of injection steam from produced water. The generation ofinjection steam from produced water is accomplished by utilizing a highpressure, high efficiency IFSG process. This overcomes the disadvantagesof the low efficiency OTSG, the requirements for treating the fullproduced water feed stream to near ASME quality standards for water tubeboilers, and high power consumption by the MVC installations. Whenincorporated with the zero liquid discharge (ZLD) in one embodiment,recoveries greater than 98% of the produced water feed stream may beattainable at a cost effective price with no liquid streams requiringdisposal.

Both the IFSG 84 and the watertube boiler 110 are operated inenvironments that they are well suited for; i.e. a high total dissolvedsolids (TDS) tubular steam generator with “pigging” capability coupledwith a high pressure high purity ASME feedwater grade watertube boileror OTSG. This leads to equipment reliability and reduced costs. The costreductions can be broken down into lower operating costs, since there isno requirement for mechanical vapor compressors, and lower waterpretreatment capital costs, since there is not a requirement forextensive water conditioning associated with changing produced waterinto ASME quality water.

With reference to FIG. 1 a mixture of oil, water, and gases is recoveredfrom a production well. The mixture of oil and water is generallyreferred to as the emulsion. The temperature of this mixture is usuallyabove 160° C.

The gases are separated from emulsion liquids in a group separator 3.The gases from the group separator 3 are cooled in heat exchanger 4A andthe emulsion liquids are cooled in heat exchanger 4B. The cooled gasbecomes produced gas. The cooled liquids, which are a mixture of oil andwater, are transferred to free water knockout (FWKO) 5.

The free water knockout 5 separates substantially all of the free oilfrom the emulsion. The separated oil becomes sales oil. The remainingliquid, which is water with between 50 ppm and 1,000 ppm of free oil isreferred to as produced water. The produced water is further cooled inglycol cooler 6.

Virtually all of the remaining free oil is removed from the producedwater in deoiling equipment 7 and becomes slops stream 300 which isdirected to stream 305 which transfers waste to multiple effectevaporator 13. Details of the multiple effect evaporator 13 are notdealt with here in detail. For a detailed and unified understanding ofthe multiple effect evaporator and how the same is used in purificationprocesses, one is directed to U.S. Pat. No. 7,578,345, the disclosure ofwhich is expressly incorporated herein by reference.

Produced water stream 14 will typically contain soluble and insolubleorganic and inorganic components. The inorganic components can be saltssuch as sodium chloride, sodium sulfate, calcium chloride, calciumcarbonate, calcium phosphate, barium chloride, barium sulfate, and otherlike compounds. Metals such as copper, nickel, lead, zinc, arsenic,iron, cobalt, cadmium, strontium, magnesium, boron, chromium, and thelike may also be included. Organic components are typically dissolvedand emulsified hydrocarbons such as benzene, toluene, phenol, and thelike.

Produced waters utilized for production of steam additionally includethe presence of silicon dioxide (also known as silica or SiO₂) in oneform or another, depending upon pH and the other species present in thewater.

For steam generation systems, scaling of the heat transfer surface withsilica is to be avoided. This is because: (a) silica forms a relativelyhard scale that reduces productivity heat transfer equipment, (b) it isusually rather difficult to remove, (c) the scale removal processproduces undesirable quantities of spent cleaning chemicals, and (d)cleaning cycles result in undesirable and unproductive off-line periodsfor the equipment. Therefore, regardless of the level of silica in theincoming raw feed water, silica is normally removed.

The deoiled produced water 14 is transferred to sorption reactor 8.Magnesium oxide (MgO) is added to sorption reactor 8. The magnesiumoxide hydrates to magnesium hydroxide. All but a few tens of ppm of thesilica in the produced water is sorbed onto the magnesium hydroxidecrystals. The magnesium hydroxide crystals with sorbed silica areremoved in ceramic membrane 9. The reject from ceramic membrane 9 isstream 301 and contains virtually all the crystals that were formed inthe sorption reactor 8. Stream 301 is directed to stream 305 whichtransfers waste streams to multiple effect evaporator 13

Permeate from the ceramic membrane is treated by ion exchange 10 toremove multi-valent cations. These cations include, but are not limitedto, calcium, magnesium, lithium, and barium. The ion exchange processesinclude but are not limited to weak acid cation (WAC), strong acidcation (SAC), or combinations of WAC and SAC.

It is noted that silica removal can be avoided by operating the IFSG ata lower conversion of water to steam and taking a higher blowdown flowfrom the steam separator or by adding a silica scale inhibitor. Ionexchange would still be used to prevent hardness based scales. Morefrequent chemical cleaning and/or pigging may be required in thisembodiment to remove soft silica scales from the IFSG.

The treated produced water from the ion exchange process is heatedagainst the oil emulsion from the wells in heat exchanger 4B and gasthat has been separated from the emulsion in heat exchanger 4A. Thisstep recovers heat that would otherwise be wasted.

After heating by the emulsion and produced gas the treated producedwater is further heated by condensate cooler 11 to approximately thesaturation temperature corresponding to the desired pressure of thesteam at the outlet of the steam separator 12. This heating isaccomplished using the condensed steam from the IFSG group 84. Thepre-heated produced water stream 85 is then discharged into the steamseparator 12 where it is mixed with the steam-water mixture from theIFSG group 84. The steam separator 12 separates the steam-water mixtureinto steam and water.

A recirculation pump 90 transfers the separated water from the outlet ofsteam separator 12 to the inlet of the IFSG group 84. The water flow tothe IFSG group can be approximately 5 times the desired amount of steamthat is generated in the IFSG group. This water is distributed betweenbanks of IFSGs so that there is approximately even flow in each coil.

Before discussing the process further, it may be beneficial to brieflyreview the structure of the ISFG 84. Basically the ISFG 84 includes oneor more containment vessels 400 as schematically illustrated in FIG. 2.The length of a containment vessel is typically between 40 feet and 120feet. Each containment vessel 400 includes a pipe or tube segment 402.The length of the tube segment in one embodiment is typically between200 feet and 1200 feet. In one embodiment, the pipe segment 402 assumesa serpentine configuration within the containment vessel 400 and as suchincludes elongated sections that turn and wind back and forth throughoutthe containment vessel 400. FIG. 2 illustrates an example of a pipesegment 402. Note that the pipe segment includes an inlet 402A and anoutlet 402B. In addition, the same pipe segment includes a plurality ofruns. In the case of the exemplary embodiment shown herein, the pipesegment includes six runs, 402C, 402D, 402E, 402F, 402G and 402H. Itshould be appreciated that the number of runs could vary depending onthe application and the capacity of the process. The pipe segment andits respective runs are supported within the containment vessel 400.Typically an internal frame structure is provided interiorly of thecontainment vessel 400 and the frame structure engages and supports thepipe segment and the runs that make up the pipe segment.

In the embodiment illustrated herein, the containment vessel is anelongated cylinder. The length of a containment vessel is typicallybetween 40 feet and 120 feet. However it should be appreciated that theshape and size of the containment vessel 400 can vary. In one exemplaryembodiment, the containment vessel 400 includes an outside diameter ofapproximately 24 inches and is constructed of schedule 80 pipe, whichcan a have typical length between 200 feet and 1200 feet. In the sameexample, the diameter of the internal pipe or tube segment is on theorder of approximately 4 inches and can also be constructed of schedule80 pipe. Again, the size and capacity of the containment vessel 400 andthe pipe segments can vary.

FIG. 2 schematically illustrates the inlet and outlets 402A and 402B ofa pipe segment associated with a single containment vessel 400. FIG. 3shows a bank of containment vessels 400 connected by one or moremanifolds 404 and 405. As seen in FIG. 3, manifold 404 is operative todirect produced water into the inlet of the respective indirect firedsteam generators 84. Manifold 405 is operatively connected to the outletof the respective indirect fired steam generators 84. This enables thesteam-water mixture in the respective indirect fired steam generators 84to be directed through the outlets thereof and to the manifold 405. Oncein the manifold 405 the steam-water mixture is directed to the steamseparator 12, or in an alternative design, the steam-water mixture couldbe directed to the injection well. It should be appreciated thatindividual containment vessels 400 can be banked together and then ifdesired, the individual banks can be operatively interconnected to formgroups. This provides an efficient and cost effective design forapplications requiring multiple containment vessels 400.

The temperatures and pressures within the containment vessel 400 andwithin the pipe segments can vary. In one exemplary embodiment, it iscontemplated that the temperature within the containment vessel 400outside of the pipe segment would be approximately 600° F. and that thepressure within the containment vessel, outside of the pipe segment,would be approximately 1500 psig. Then inside the pipe segments it iscontemplated that the temperature would, in one example, beapproximately 520° F. and the pressure would be approximately 800 psig.

Steam from a water tube drum boiler 110 is directed to the containmentvessels in the IFSG group 84 and condenses on the outside of the coil orpipe segments. The latent heat of vaporization transfers through thewall of the pipe and into the mixture inside the pipe, thereby raisingthe temperature of the mixture. At the high temperature and pressure inthe pipe a small increase in temperature causes a large increase inpressure and the mixture quickly reaches its bubble point. After thebubble point is reached the heat transferred from the condensing steamon the outside of the pipe boils water from the mixture inside the coil.The two phase mixture of steam and water exits the IFSG group 84 throughstream 88 and then enters steam separator 12. Various types of boilerscan be utilized to produce steam that is utilized by the IFSG group 84.In one example, the boiler may include a heat recovery steam generatorwhich could be heated by a combustion turbine exhaust. In this example,the combustion turbine is connected to an electrical generator.

The vapor in stream 88 is separated in steam separator 12 and becomes98% or higher quality steam. This steam at the high pressure necessaryfor injection, and typically with less than 10 ppm of non-volatilesolutes, is routed through line 100 directly to the steam injectionwells.

In the steam separator 12, the liquid from stream 88 mixes with thetreated and conditioned produced water stream 85. Stream 85 dilutes theconcentrated high solids stream present in line 88. Stream 94 isrecirculated with high pressure recirculation pump 90. A portion ofstream 94 is removed as IFSG blowdown through line 96. Stream 96contains the solutes that were present in stream 85.

A commercial watertube drum boiler 110 operating on high quality ASMErated feed water supplies the high pressure steam 124 that is requiredto drive the high pressure high efficiency IFSG 84. The high pressuresteam 124 transfers heat by condensing on the outside of the pipe of theIFSG 84. The condensing steam descends by gravity to the bottom of thecontainment vessel 400 and is collected as condensate stream 120.Condensate stream 120 is used to preheat treated and conditionedproduced water in condensate cooler 11.

The condensate from condensate cooler 11 is further cooled in boilerfeed water heater 2 before flashing to slightly above atmosphericpressure in Flash Tank 15. The cooled condensate is purified incondensate polisher Ion exchange 200. Make-up water is added tocondensate polisher ion exchange 200 to replace boiler blowdown 114.After deaeration in deaerator 16 the purified condensate is thenreturned via line 204 to the commercial watertube boiler 110 whereinenergy is supplied and the condensate is returned to steam.

A small boiler blowdown stream represented by line 114 is taken from thewatertube boiler 110, and directed to either waste or, in oneembodiment, to an evaporator through line 305 for recovery. The blowdownstream 114 is necessary to prevent buildup of total dissolved solids(TDS) in the boiler 110 and is typically less than 2.5% of the boilercapacity.

Makeup water for the watertube boiler 110 can be supplied by any ofvarious means of producing deionized water. As depicted in FIG. 1, themakeup is supplied through line 204 by a condensate polishing unit 200.The condensate polishing system can be of various types to removesolutes from both the condensate stream 120 and from the make-up watersource, such as well water. Under these circumstances, the unit 200provides high quality ASME grade water, which along with a high pressureboiler chemical program 112, generally ensures trouble free operation ofthe watertube boiler 110. In other embodiments, the condensate polishingunit 200 can be replaced with a reverse osmosis system or a combinationof reverse osmosis and ion exchange to provide the ASME quality waterrequired by watertube boiler 110.

The steam separator blowdown stream 96 is flashed in flash tank 130. Theflash steam is used to drive a multiple effect evaporator 13 to maximizewater recovery and waste disposal requirements. Some of the dissolvedsalts will precipitate in the multiple effect evaporator 13. Additionalsuspended material will be present in streams 300 and 301. These solidsare removed from the evaporator concentrate 306 in centrifuge 17. Thecentrate 307 from centrifuge 17 can be disposed in a deep well orfurther processed in a zero liquid discharge system. The combineddistillate 310 from multiple effect evaporator 13 is returned to theproduced water line downstream of ceramic membrane 9.

The just described IFSG process produces a high quality steam atpressures dependent on the individual site designs, typically rangingfrom 200 to 900 psig, which satisfies the near 100% quality steamrequirement needed for SAGD operation at a cost reduction when comparedto OTSG and MVC processes.

FIG. 1A depicts a process similar to that shown in FIG. 1 and describedabove. The basic differences between the processes of FIGS. 1 and 1A liein how the produced water stream 85 is ultimately directed to the steamseparator 12 and IFSG 84. In the process of FIG. 1 the produced waterstream 85 is directed initially into the steam separator 12. At least aportion of that produced water is returned through line 94 to the IFSGwhere the water passing through the IFSG is heated and converted to asteam-water mixture.

In the embodiment depicted in FIG. 1A, the produced water stream 85 isfirst directed to the IFSG 84. As shown in FIG. 1A, produced waterleaving the condensate cooler 11 is directed in stream 85 to the inletof IFSG 84. As shown in FIG. 1A the produced water stream 85 joins theseparated water return stream 94 and both streams are directed throughthe IFSG where the water is heated and converted to a steam-watermixture. As noted above, some of the produced water in stream 85 willeventually be separated by the steam separator 12 and recycled back tothe IFSG via line 94.

The present invention may, of course, be carried out in other specificways than those herein set forth without departing from the scope andthe essential characteristics of the invention. The present embodimentsare therefore to be construed in all aspects as illustrative and notrestrictive and all changes coming within the meaning and equivalencyrange of the appended claims are intended to be embraced therein.

1. A method of recovering oil from an oil well and producing steam forinjection into an injection well, the method comprising: a. recoveringan oil-water mixture from the oil well; b. separating oil from theoil-water mixture to produce an oil product and produced water; c.directing the produced water to an indirect fired steam generator; d.directing the produced water through one or more heating tubes in theindirect fired steam generator; e. generating steam in a boiler; f.directing the steam from the boiler to the indirect fired steamgenerator and heating the water passing through the tubes of theindirect fired steam generator to produce a steam-water mixture; g.directing the steam-water mixture from the indirect fired steamgenerator to a steam separator; h. wherein the steam separator separateswater from the steam and the separated water is directed from the steamseparator to the indirect fired steam generator; and i. directing thesteam from the steam separator to the injection well.
 2. The method ofclaim 1 wherein the one or more tubes is held within a containmentvessel and the steam from the boiler is contained in the vessel underpressure and occupies a space exteriorly of the one or more tubes. 3.The method of claim 1 wherein the steam from the boiler condenses in theindirect fired steam generator and forms a condensate, and the methodincludes treating the condensate to remove impurities and directing thetreated condensate to the boiler where the treated condensate isutilized to form steam.
 4. The method of claim 3 including transferringheat from the condensate to the produced water and heating the producedwater prior to the produced water reaching the indirect fired steamgenerator.
 5. The method of claim 1 wherein the method recovers 95% ormore of the produced water.
 6. The method of claim 1 including treatingthe produced water prior to the produced water reaching the indirectfired steam generator or the steam separator by precipitating silica inthe water and removing the precipitated silica by a membrane separationprocess.
 7. The method of claim 6 including mixing magnesium oxide orother metal oxide with the produced water to form magnesium hydroxidecrystals and sorbing silica onto the magnesium hydroxide crystals. 8.The method of claim 7 including filtering the produced water with aceramic membrane and filtering the magnesium hydroxide crystals withsorbed silica from the produced water with the ceramic membrane.
 9. Themethod of claim 6 wherein after removing the silica from the producedwater, passing the produced water through an ion exchange and removinghardness from the produced water.
 10. The method of claim 1 includingheating the produced water prior to reaching the indirect fired steamgenerator or the steam separator to a temperature of approximately 380°F. to approximately 540° F.
 11. The method of claim 1 including heatingthe produced water to approximately a saturation temperaturecorresponding to a selected pressure of the steam produced by theindirect fired steam generator and then directing the produced water tothe steam separator.
 12. The method of claim 1 wherein the separatedwater flowing between the steam separator and the indirect fired steamgenerator is approximately 5 to 10 times the amount of steam produced bythe indirect fired steam generator.
 13. The method of claim 1 whereinthe indirect fired steam generator comprises a containment vessel withthe one or more heating tubes extending within the containment vessel;and wherein the temperature within the containment vessel outside of theone or more heating tubes is approximately 460° F. to 660° F. andwherein the pressure within the containment vessel outside of the one ormore heating tubes is approximately 450 psig to approximately 2350 psig.14. The method of claim 13 wherein the method is operated such that thetemperature inside the one or more heating tubes is approximately 400°F. to approximately 600° F. and the pressure inside the one or moreheating tubes is approximately 250 psig to approximately 1500 psig. 15.The method of claim 1 including contacting the one or more heating tubeswith the steam from the boiler and condensing the steam on the outsideof the one or more heating tubes, giving rise to the latent heat ofvaporization transferring through the one or more heating tubes andincreasing the temperature of the steam-water mixture in the one or moreheating tubes.
 16. The method of claim 1 including pre-treating theproduced water prior to reaching the indirect fired steam generator orthe steam separator to remove substantial solids from the producedwater; wherein the steam-water mixture produced by the indirect firedsteam generator contains relatively more solids than the produced waterprior to reaching the indirect fired steam generator or the steamseparator; and the method includes diluting the solids in thesteam-water mixture by mixing the produced water with the steam-watermixture.
 17. The method of claim 1 wherein prior to entering the steamseparator, the produced water is directed into the indirect fire steamgenerator, and wherein water is separated from the steam-water mixturein the steam separator and wherein the separated water is directed intothe indirect fire steam generator.
 18. The method of claim 1 whereinprior to entering the indirect fired steam generator the produced wateris directed into the steam separator, and wherein produced water isseparated from the steam-water mixture in the steam separator andwherein the separated water is directed into the indirect fired steamgenerator.
 19. A system for producing steam for use in an oil recoveryprocess where the produced steam is injected into an injection well, thesystem comprising: a. a steam separator for separating a steam-watermixture into steam and water; b. the steam separator including an inlet,a steam outlet, and a separated water outlet; c. an indirect fired steamgenerator operatively connected to the steam separator and including acontainment vessel having one or more heating tubes extending throughthe containment vessel; d. a line operatively interconnected between theindirect fired steam generator and the steam separator for directing asteam-water mixture from the indirect fired steam generator to the steamseparator; e. a separated water line extending from the separated wateroutlet of the steam separator to an inlet of the indirect fired steamgenerator for directing separated water from the steam separator to theinlet of the indirect steam generator and into the heating tubesthereof; f. a boiler for producing steam for heating the heating tubesextending through the containment vessel of the indirect fired steamgenerator; and g. a steam transfer line operatively interconnectedbetween the boiler and the containment vessel of the indirect firedsteam generator for directing steam from the boiler into the containmentvessel of the indirect fired steam generator.
 20. The system of claim 19further including an evaporator for receiving separated water from thesteam separator and treating the separated water with the evaporator.21. The system of claim 20 where the evaporator is a multiple effectevaporator.
 22. The system of claim 21 where heating steam for themultiple effect evaporator is generated by partially flashing theseparated water from the steam separator before said water enters themultiple effect evaporator.
 23. The system of claim 19 including aproduced water pretreatment subsystem located upstream from the steamseparator for removing silica and other dissolved solids from theproduced water prior to the produced water reaching the indirect firedsteam generator or steam separator.
 24. The system of claim 23 whereinthe pretreatment subsystem includes a de-oiler for removing oil from theproduced water, a reactor for holding the produced water such that areagent can be mixed therewith, a membrane separation unit for filteringthe produced water, and an ion exchange unit for removing hardness fromthe produced water.
 25. The system of claim 19 including a condensatetreatment subsystem for receiving condensate from the containment vesselof the indirect fired steam generator and treating the condensate toremove impurities from the condensate and directing the treatedcondensate back to the boiler where the treated condensate is convertedto steam.
 26. An indirect fired steam generator for heating water andproducing a steam-water mixture, comprising: a containment structurehaving a length of approximately 80 feet to approximately 1200 feet andhaving a surrounding wall structure that defines an interior space forreceiving and holding steam under pressure; a network of one or moreelongated heating tubes extending back and forth through the interior ofthe containment structure and wherein there is provided an open spacebetween the network of heating tubes and the surrounding wall structureof the containment structure such that the heating tubes are configuredsuch that when the containment structure holds steam the network ofheating tubes extend back and forth through the steam held within thecontainment structure; and wherein the network of heating tubes includesan inlet for receiving water and an outlet for directing a steam-watermixture from the indirect fired steam generator.
 27. The indirect firedsteam generator of claim 26 wherein the network of heating tubesincludes a plurality of runs where each run extends between oppositeends of the containment structure.
 28. The indirect fired steamgenerator of claim 26 wherein the network of elongated heating tubesincludes a heating tube having an inlet and an outlet and wherein theheating tube has a length of approximately 200 feet to approximately1200 feet and includes multiple runs such that the multiple runs of theheating tube zigzags back and forth through the containment structure.29. The indirect fired steam generator of claim 26 wherein thecontainment structure comprises an elongated cylinder and wherein thenetwork of heating tubes includes a plurality of heating tube segmentswhere each heating tube segment assumes a generally cylindrical shape.30. The indirect fired steam generator of claim 29 wherein the diameterof the cylindrical containment structure is approximately 4 to 5 timeslarger than the diameter of the respective heating tube segments thatextend through the cylindrically shaped containment structure.
 31. Theindirect fired steam generator of claim 26 wherein the indirect firedsteam generator forms one of a bank of indirect fired steam generatorswith each indirect fired steam generator of the bank including at leastone network of heating tubes; and wherein the network of heating tubesdisposed in the indirect fired steam generators are operativelyinterconnected such that water or a steam-water mixture flows from amanifold into each of the indirect fired steam generators and the wateror steam-water mixture therein is heated in the indirect fired steamgenerators as the water or steam-water mixture flows through therespective networks of heating tubes; and wherein the outlet from eachindirect fired steam generator is operatively connected to a collectionmanifold.
 32. The indirect fired steam generator of claim 26 wherein theindirect fired steam generator comprises a containment vessel with theone or more heating tubes extending within the containment vessel; andwherein the temperature within the containment vessel outside of the oneor more heating tubes is approximately 460° F. to 660° F. and whereinthe pressure within the containment vessel outside of the one or moreheating tubes is approximately 450 psig to approximately 2350 psig. 33.The indirect fired steam generator of claim 26 wherein the indirectfired steam generator comprises a containment vessel with the one ormore heating tubes extending within the containment vessel; and whereinthe temperature within the heating tubes is approximately 400° F. toapproximately 600° F. and the pressure inside the one or more heatingtubes is approximately 250 psig to approximately 1500 psig.
 34. A methodof recovering oil from an oil well and producing steam for injectioninto an injection well, the method comprising: a. recovering anoil-water mixture from the oil well; b. separating oil from theoil-water mixture to produce an oil product and produced water; c.directing the produced water first into and through an indirect firedsteam generator or first into a steam separator; d. generating steam ina boiler; e. directing the steam from the boiler to the indirect firedsteam generator and heating water passing through tubes of the indirectfired steam generator to produce a steam-water mixture; f. when theproduced water is first directed into the indirect fire steamgenerator:
 1. heating the produced water and producing the steam-watermixture;
 2. directing the steam-water mixture from the indirect firedsteam generator into the steam separator;
 3. separating the steam-watermixture into steam and water;
 4. recycling separated water from thesteam separator back to the indirect fired steam generator;
 5. directingsteam separated by the steam separator into the injection well; and g.when the produced water is first directed into the steam generator: a.separating the steam-water mixture in the steam separator into steam andwater; b. directing the separated water from steam separator to theindirect fire steam generator; c. heating the separated water in theindirect fired steam generator to produce the steam-water mixture; d.directing the steam-water mixture from the indirect fired steamgenerator into the steam separator; and e. directing the separated steamfrom the steam separator into the injection well.
 35. A method ofrecovering oil from an oil well and producing steam for injection intoan injection well, the method comprising: a. recovering an oil-watermixture from the oil well; b. separating oil from the oil-water mixtureto produce an oil product and produced water; c. directing the producedwater to and through an indirect fired steam generator; d. directing theproduced water through one or more heating tubes in the indirect firedsteam generator; e. directing a stream of water to a boiler that isindependent of the indirect fired steam generator; f. generating steamin the boiler; g. directing the steam from the boiler to the indirectfired steam generator and heating the water passing through the tubes ofthe indirect fired steam generator to produce a steam-water mixture; andh. directing at least a portion of the steam-water mixture from theindirect fired steam generator into the injection well.
 36. The methodof claim 35, including condensing the steam in the indirect fired steamgenerator to form a condensate; treating the condensate to removeimpurities; and directing the treated condensate to the boiler where thetreated condensate is utilized to form steam.
 37. The method of claim36, including transferring heat in the condensate to the produced waterand heating the produced water prior to the produced water beingdirected into the indirect fired steam generator.
 38. The method ofclaim 35, including directing the steam-water mixture from the indirectfired steam generator to a steam separator and separating thesteam-water mixture into steam and water and recycling at least aportion of the separated water back to the indirect fired steamgenerator and directing the separated steam into the injection well. 39.The method of claim 1 wherein the boiler includes a heat recovery steamgenerator, and wherein the heat recovery steam generator generates steamthat is directed to the indirect fired steam generator.
 40. The methodof claim 39 wherein the heat recovery steam generator is heated bycombustion turbine exhaust.